Marc Henneaux Collège de France Champs, cordes et gravité Année 2022-2023 La structure asymptotique de l'espace-temps (II) Séminaire - Glenn Barnich : Coadjoint Representation and Geometric Action for the BMS Group The coadjoint representation of the BMS4 group is constructed and related to the conserved current algebra of non-radiative asymptotically flat spacetimes at null infinity. The associated geometric action is a field theory in two plus one dimensions whose Poisson bracket algebra of Noether charges realizes the BMS4 Lie algebra. Glenn Barnich, Université Libre de Bruxelles, Belgique